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A flexible, intelligent supercapacitor is designed and fabricated using a smart gel polymer electrolyte (GPE) and redox-activated electrodes. This flexible, intelligent supercapacitor exhibits superior electrochemical, self-healing, and deformation-responsive properties. Methylene blue (MB) and Na2MoO4 are added to the self-healing gel of PVA–H3BO3–H2SO4 (PS) to generate smart GPE PVA–H3BO3–H2SO4–MB–Na2MoO4 (PSMMo) with temperature and deformation sensitivity. The response current of smart GPE PSMMo exhibits a positive correlation with the working temperature. The bending process induces peak current generation, whose variation in magnitude depends on the bending degree. Na2MoO4, MB, and polyaniline (PANI) are used to modify activated carbon paper (ACP) to form Na2MoO4–ACP and MB–PANI–ACP redox-activated electrodes, which are combined with smart GPE PSMMo to form an intelligent supercapacitor. The matching faradaic reaction of Na2MoO4–ACP, MB–PANI–ACP electrodes and PSMMo electrolyte provides the interfacial redox reactivity to contribute to superior pseudocapacitance. The Na2MoO4–ACP supercapacitor (83.93 mF cm−2) and MB–PANI–ACP supercapacitor (250.23 mF cm−2) have obviously much higher specific capacitance than the ACP supercapacitor (53.42 mF cm−2) and PANI–ACP supercapacitor (141.78 mF cm−2). The MB–PANI–ACP supercapacitor has an energy density of 681.18 mW h m−2 at 0.5 mA cm−2. Theoretical simulation calculations verify the contribution of redox-activated electrodes to electrochemical performance. The smart GPE PSMMo-based supercapacitor exhibits self-healing, deformation response and faradaic capacitance contribution properties which are far superior to those of a normal GPE-based supercapacitor with self-healing properties. [ABSTRACT FROM AUTHOR]

The redox additive KI-modified and H2SO4-protonated polyvinyl alcohol gel polymer electrolyte (KI-H2SO4-PVA GPE) is used to match well with an activated carbon paper (ACP) electrode, which is adopted for solid-state pseudocapacitor applications. Enhanced hydrogen bonding interactions are established between oxygen-containing functional groups of ACP and multi-hydroxyl groups of PVA, promoting interfacial charge transfer. An intensified electrostatic adsorption is also promoted between H2SO4-protonated PVA and free iodide anions, enhancing the ionic and electrical conductivity of GPE. The electroactive iodide anion with polyvalent states of I−, I3− and IO3− in KI-H2SO4-PVA GPE participates in reversible redox reactions at the ACP electrode interface, which mostly contributes to Faradaic capacitance. The mass ratio of redox additive KI was optimized to be 0.166, which could balance the capacitance and the cyclability of KI-H2SO4-PVA GPE. The KI-H2SO4-PVA GPE reveals lower ohm resistance, charge transfer resistance and Warburg impedance, leading to its higher electrical and ion conductivity compared to H2SO4-PVA GPE. Theoretical simulations proved that the protonation of H2SO4-PVA and electrostatic interaction between H2SO4-protonated PVA and KI could cause an effective decrease in the interfacial energy of the activated carbon paper electrode. The KI-H2SO4-PVA GPE/ACP accordingly presents higher specific capacitance (24.75 mF cm−2) and rate capability (45.5%) than H2SO4-PVA GPE/ACP (12.93 mF cm−2, 15.6%). The redox-activated KI-H2SO4-PVA GPE exhibits a lowered cycling stability (64.5%) compared to H2SO4-PVA GPE (78.3%) in ACP supercapacitor applications due to the gradually decreasing irreversibility of the redox reactions of polyvalent iodide ions. The KI-H2SO4-PVA GPE matches well with ACP electrode and accordingly is suitable for solid-state pseudocapacitor applications with high capacitance performance. The KI-modified and H2SO4-protonated polyvinyl alcohol gel polymer electrolyte (KI-H2SO4-PVA GPE) is used to match well with the hydroxyl and epoxy groups activated carbon paper (ACP) electrode to form the intensified hydrogen bonding interface, contributing to superior Faradaic capacitance for the solid-state supercapacitor application. [ABSTRACT FROM AUTHOR]